<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>flex test</title>
  <style>
    html, body {
      height: 100%;
      width: 100%;
      padding: 0;
      margin: 0;
    }
    .wrap {
      display: flex;
      flex-direction: column;
      color: white;
      text-align: center;
      height: 100%;
    }
    .header {
      height: 50px;
      background: green;
    }
    .body {
      flex: 1;
      background: rebeccapurple;
    }
  </style>
</head>
<body>
  <div class="wrap">
    <div class="header">
      header
    </div>
    <div class="body">
      body
      <div style="height: 900px; width: 200px; background-color: yellow;">
        padding
      </div>
    </div>
  </div>
</body>
</html>
